A centrifugal separator of this kind is shown and described in U.S. Pat. No. 3,685,721. Within the rotor of this known centrifugal separator four conveyor screws are arranged. Each one of these has or is connected with a transmission shaft of the above mentioned kind, which extends out through one of the rotor end walls.
If the rotor in a centrifugal separator of this kind is to be caused to rotate at a very high rotational speed for accomplishing high separation efficiency, rotation of the conveyor screws relative to the rotor will encounter a large resistance, and the bearings through which the transmission shafts are journalled in the rotor will be strongly loaded, especially because the conveyor screws as well as their transmission shafts have to rotate at a high speed in a path at a large distance from the rotational axis of the rotor. A problem in this connection is to maintain in said bearings, which in their entirety rotate around the rotational axis of the rotor, the necessary amount of lubricant during a long time of operation for the rotor.
The object of the present invention is to provide an arrangement which is as advantageous as possible as to the operation conditions for the said bearings, as a consequence of the fact that these together with the transmission shafts rotate during operation of the rotor around the rotational axis of the rotor.
According to the invention this object may be achieved in a centrifugal separator of the initially defined kind in a way such that the rotor delimits a transmission chamber that is liquid tightly separated from the separation chamber and that the rotor is formed to maintain in the transmission chamber during rotation of the rotor an auxiliary liquid in contact with at least part of each one of said bearings.
In this way the said bearings, which are preferably constituted by slide bearings, may be constantly lubricated by said auxiliary liquid. This may preferably be constituted by water. The transmission chamber, which preferably is annular and is delimited between said one end wall and a further wall extending around the rotational axis of the rotor, may have an overflow outlet for said auxiliary liquid.
In an advantageous embodiment of the invention each transmission shaft supports a bearing member in the transmission chamber, which has a bearing surface extending around the transmission shaft along a circle having a substantially larger diameter than that of said openings in the rotor end wall, through which the transmission shaft extends. Hereby, the pressure per unit of surface in each bearing will become somewhat reduced. Furthermore, a relatively large part of each bearing member will be immersed in auxiliary liquid in the transmission chamber and, thereby, be acutated during rotation of the rotor by a hydraulic force directed towards the rotational axis of the rotor. This force results in a certain unloading of the bearing.
Preferably, said bearing members are used also for transmission of rotational movement from a central transmission member in the rotor to said transmission shafts. Then, it is desirable that the transmission forces being transferred are acting as close to the bearings of the transmission shafts as possible. According to the invention each bearing member, therefore, has a surrounding part, which has an inside with a bearing surface facing the transmission shaft and also an outside through which it engages with the central transmission member. This engagement may be direct, e.g. through cogs, or indirect, e.g. through a tooth belt. In both cases the said surrounding part should be in a driving engagement with the central transmission member in an axial plane that substantially coincides with an axial plane through said bearing surface of the surrounding part.